```html
<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>克隆图算法可视化</title>
    <link href="https://cdn.staticfile.org/font-awesome/6.4.0/css/all.min.css" rel="stylesheet">
    <link href="https://cdn.staticfile.org/tailwindcss/2.2.19/tailwind.min.css" rel="stylesheet">
    <link href="https://fonts.googleapis.com/css2?family=Noto+Serif+SC:wght@400;500;600;700&family=Noto+Sans+SC:wght@300;400;500;700&display=swap" rel="stylesheet">
    <script src="https://cdn.jsdelivr.net/npm/mermaid@latest/dist/mermaid.min.js"></script>
    <style>
        body {
            font-family: 'Noto Sans SC', Tahoma, Arial, Roboto, "Droid Sans", "Helvetica Neue", sans-serif;
            color: #333;
            background-color: #f9fafb;
            line-height: 1.6;
        }
        .hero-gradient {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
        }
        .code-block {
            background-color: #2d3748;
            border-radius: 0.5rem;
            box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
        }
        .algorithm-card:hover {
            transform: translateY(-4px);
            box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
        }
        .highlight {
            position: relative;
        }
        .highlight::after {
            content: '';
            position: absolute;
            bottom: 0;
            left: 0;
            width: 100%;
            height: 40%;
            background-color: rgba(167, 139, 250, 0.3);
            z-index: -1;
            transform: rotate(-1deg);
            transition: all 0.3s ease;
        }
        .highlight:hover::after {
            height: 50%;
            background-color: rgba(167, 139, 250, 0.4);
        }
    </style>
</head>
<body class="antialiased">
    <!-- Hero Section -->
    <section class="hero-gradient text-white py-20 px-4 md:px-8">
        <div class="container mx-auto max-w-6xl">
            <div class="flex flex-col md:flex-row items-center">
                <div class="md:w-1/2 mb-10 md:mb-0">
                    <h1 class="text-4xl md:text-5xl font-bold mb-6 leading-tight font-serif">
                        <span class="highlight">克隆图</span>算法解析
                    </h1>
                    <p class="text-xl md:text-2xl opacity-90 mb-8 leading-relaxed">
                        深度探索图的深拷贝原理与应用，掌握DFS与BFS两种经典解法
                    </p>
                    <div class="flex space-x-4">
                        <div class="flex items-center">
                            <i class="fas fa-code text-purple-200 mr-2 text-lg"></i>
                            <span class="font-medium">算法实现</span>
                        </div>
                        <div class="flex items-center">
                            <i class="fas fa-chart-line text-purple-200 mr-2 text-lg"></i>
                            <span class="font-medium">复杂度分析</span>
                        </div>
                        <div class="flex items-center">
                            <i class="fas fa-project-diagram text-purple-200 mr-2 text-lg"></i>
                            <span class="font-medium">可视化展示</span>
                        </div>
                    </div>
                </div>
                <div class="md:w-1/2">
                    <div class="mermaid p-6 bg-white bg-opacity-10 rounded-xl border border-white border-opacity-20">
                        graph LR
                            A[原始节点1] --> B[节点2]
                            A --> C[节点4]
                            B --> D[节点3]
                            C --> D
                    </div>
                </div>
            </div>
        </div>
    </section>

    <!-- Problem Section -->
    <section class="py-16 px-4 md:px-8 bg-white">
        <div class="container mx-auto max-w-4xl">
            <div class="flex items-center mb-8">
                <div class="w-2 h-10 bg-purple-600 rounded-full mr-4"></div>
                <h2 class="text-3xl font-bold font-serif">题目描述</h2>
            </div>
            <div class="prose max-w-none text-gray-700">
                <p class="text-lg leading-relaxed">
                    给定无向连通图中一个节点的引用，请你返回该图的<strong class="text-purple-600">深拷贝</strong>。
                    图中的每个节点都包含它的值 <code class="bg-gray-100 px-2 py-1 rounded">val</code> 和其邻居列表。
                </p>
                <div class="bg-blue-50 border-l-4 border-blue-500 p-4 my-6 rounded-r">
                    <div class="flex">
                        <div class="flex-shrink-0">
                            <i class="fas fa-info-circle text-blue-500 text-xl"></i>
                        </div>
                        <div class="ml-3">
                            <p class="text-sm text-blue-700">
                                示例：